Ask a window salesman whether you need triple glazing and the answer is usually whatever earns the bigger commission. Ask a glazier who fits both across London every week and you get a more useful answer: it depends on your house, your street and how long you're staying, and here are the actual numbers.
Quick answer
For most London homes, modern double glazing (U-value 1.2-1.4 W/m²K) is the value choice; triple glazing (0.6-0.8) costs 15-25% more and saves only £30-£80 a year in energy. Choose triple for comfort in rooms you live in, very exposed or north-facing elevations, or deep-retrofit projects, not for noise, where secondary glazing or acoustic glass does the job better.
What's the real difference between double and triple glazing?
Double glazing is two panes with one insulating cavity; triple glazing is three panes with two. Each cavity, typically 12-20mm, filled with argon and bounded by a low-emissivity (low-E) coated pane, slows heat transfer. Adding the third pane adds a second cavity and a second low-E coating, roughly halving the heat loss of the unit.
It also adds thickness and weight: a typical double unit is 24-28mm and a triple unit 36-44mm, weighing about 50% more. That matters because it dictates frames, hinges and hardware: you can't usually drop triple units into frames designed for double, which is why triple glazing is priced as a whole-window decision rather than a glass swap.
U-values compared: single vs double vs triple
The U-value measures heat loss through the window in watts per square metre per degree (lower is better). Here's the honest league table, including the options nobody selling triple glazing mentions:
| Glazing type | Typical U-value (W/m²K) | Inner glass on a 0°C night | Verdict |
|---|---|---|---|
| Single glazing | ~5.8 | Ice cold (~5-8°C), streams with condensation | Upgrade from this is transformative, whatever you choose |
| Old double (air-filled, pre-2002) | 2.6-2.8 | Cool, condensates on cold mornings | Worth replacing: units this age are often failing anyway |
| Modern double (low-E, argon) | 1.2-1.4 | Mildly cool (~15-17°C) | The value sweet spot; meets Building Regs (≤1.4) |
| Best double (soft-coat low-E, warm-edge) | ~1.1 | Comfortable | Closes most of the gap to triple for less money |
| Triple glazing | 0.6-0.8 | Near room temperature (~18°C) | Best comfort & efficiency; the premium buys comfort, not payback |
Notice the pattern: the leap from single (5.8) to modern double (1.2-1.4) cuts heat loss by roughly 75-80%. The further step to triple cuts what remains by about half, a real improvement, but of a much smaller number. Diminishing returns are the whole story of this comparison.
The noise myth: triple glazing isn't automatically quieter
An extra pane does not equal extra quiet, and on some frequencies standard triple glazing performs no better than good double. Sound insulation depends on mass, asymmetry and gap width, not pane count. Three identical 4mm panes separated by identical gaps can resonate together, which is why lab ratings for standard triple units sit within a decibel or two of quality double units.
If traffic, flight paths or a busy North London high street are your real problem, spend the money on acoustics instead:
- Asymmetric glass, say a 6mm outer and 4mm inner pane, so the two panes damp different frequencies.
- Acoustic laminated glass, where a flexible interlayer absorbs sound energy rather than transmitting it.
- Secondary glazing, a second, independent window with a 100mm+ air gap. It's the single most effective noise treatment we install, cutting noise by up to 70-80% (typically 40-45dB reduction), and it's often the only option allowed in conservation areas and listed buildings.
Buy triple glazing for warmth. Buy asymmetric or secondary glazing for silence. They are different problems with different answers.
The cost-payback maths, honestly
Triple glazing typically costs 15-25% more than an equivalent double glazed installation, and the extra energy saving is modest. Moving from modern double to triple in an average three-bed London home saves roughly £30-£80 a year at 2026 energy prices, meaning the premium can take 15-25 years to pay back, longer than many owners keep the house and approaching the service life of the units themselves.
So why does anyone buy it? Because payback isn't the only ledger:
- Comfort is immediate. Inner glass near room temperature means no cold radiant zone beside the window, so you can actually use the seat by the bay.
- Condensation drops sharply, because the inner pane rarely falls below dew point (our condensation guide explains why).
- Heating runs shorter cycles and rooms hold heat longer after the boiler stops.
- Future-proofing: heat-pump systems run at lower flow temperatures and reward a well-sealed envelope; EPC and regulation direction keeps tightening.
If you're replacing single glazing or blown 1990s units, the honest advice is that either choice will feel dramatic, so let the room-by-room case, not the brochure, decide.
When triple glazing makes sense in London
We recommend triple glazing selectively, and often mix it with double in one house. The cases where it earns its premium:
- North-facing and exposed elevations, corner plots, hilltop streets, riverside blocks where windows never see direct sun.
- Rooms where you sit still for hours: home offices, nurseries, bedrooms, anywhere a cold window surface is felt all day.
- Deep retrofits chasing serious efficiency (EnerPHit/Passivhaus-adjacent projects), where the whole envelope is being upgraded together.
- Forever homes: if you'll be there 20+ years, the payback objection weakens and the comfort case compounds.
- Large glazed areas: big sliders and full-height glazing lose heat in proportion to their size, so the better U-value works harder.
Where we'd steer you away: rental properties (double meets regs at lower cost), heritage frontages where slim sightlines matter, and any budget where triple glazing would crowd out more effective spending like loft insulation or draught-proofing.
Frames matter as much as the glass
Made in our own factory, no middleman
A 0.7 U-value unit in a leaky, poorly reinforced frame is wasted money: the whole-window figure is what you live with. That's why we control both halves: our uPVC windows and doors are fabricated to measure by our sister company Prime Fabrication, factory-direct, no middleman, with multi-chambered profiles and reinforcement specified for the weight of the unit you choose, double or triple.
Fabricating in-house also means the triple glazing premium is smaller with us than through installers buying frames at trade-counter mark-ups, and every installation is FENSA-certified with a made-to-measure lead time of typically 7-10 days.
Double vs triple glazing FAQs
Is triple glazing worth it in the UK?
Is triple glazing quieter than double glazing?
What is a good U-value for windows?
Can I fit triple glazing in my existing frames?
How much more does triple glazing cost than double?
Does triple glazing stop condensation?
Get both prices, decide with numbers.
Free survey across Central & North London: we measure, quote double and triple side by side, and tell you honestly which rooms justify which. FENSA-certified installation, frames from our own factory.